Schism Tracker is a free and open-source reimplementation of Impulse Tracker, a program used to create high quality music without the requirements of specialized, expensive equipment, and with a unique "finger feel" that is difficult to replicate in part. The player is based on a highly modified version of the ModPlug engine, with a number of bugfixes and changes to improve IT playback.
Where Impulse Tracker was limited to i386-based systems running MS-DOS, Schism Tracker runs on almost any platform that SDL supports, and has been successfully built for Windows, Mac OS X, Linux, FreeBSD, OpenBSD, AmigaOS, BeOS, and even the Wii. Schism will most likely build on any architecture supported by GCC4 (e.g. alpha, m68k, arm, etc.) but it will probably not be as well-optimized on many systems.
The bleeding-edge current source can be downloaded using Git:
git clone https://github.com/schismtracker/schismtracker
Those interested in development can also point a web browser at the repository to browse the source tree, change logs, etc.
You might also want to peruse the build notes for Windows, OS X, or Linux.